vlan: fix convertion to net_device_ops

commit 656299f7
(vlan: convert to net_device_ops) added a net_device_ops
with a NULL ndo_start_xmit field.

This gives a crash in dev_hard_start_xmit()

Fix it using two net_device_ops structures, one for hwaccel vlan,
one for non hwaccel vlan.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>